The present application relates to hook blocks that are used at the end of one or more wire ropes of a crane boom or luffing jib to lift heavy loads. More specifically, the present application relates to a hook block assembly capable of being assembled with different numbers and types of components to assemble different hook blocks customized for different loads. The various embodiments disclosed herein include improvements that facilitate reeving wire rope through the sheaves of the hook block by helping to immobilize and stabilize pieces that normally move during lifting operation.
The hook block acts as a block and tackle, and more specifically, as a compound pulley system because of the multiple sheaves used. Pulleys are used to change the direction of an applied force, transmit rotation motion, or realize a mechanical advantage in either a linear or rotational system of motion. A wire rope is used with a crane hook block because wire rope can withstand great tension under heavy loads. Sets of sheaves are located within housings of the hook block. Sheaves are wheels having a groove between two flanges around the circumference of the wheel.
In equilibrium, the total force on a basic pulley is zero. This means that the force on the axle of the pulley is shared equally by the two lines looping through the pulley. For the case where the lines are not parallel, the tensions in each line are still equal, but now the vector sum of all forces is zero. A second basic equation for the basic pulley follows from the conservation of energy: the product of the weight lifted times the distance it is moved is equal to the product of the lifting force (the tension in the lifting line) times the distance the lifting line is moved. The weight lifted divided by the lifting force is the advantage of the pulley system. Note that a system of pulleys does not change the amount of work done. The work is given by the force times the distance moved. The pulley simply allows trading force for distance: you pull with less force, but over a longer distance.
The term reeve means to pass a rope through a hole, ring, pulley, or block. In order to reeve the sheaves of a hook block, the hook block is often placed in an upright standing position, laid down horizontally, or in some cases it can be laid back over against the hook holding it up at some angle. Any maneuvering of the hook block is typically done with lifting equipment because, when fully assembled, a larger hook block can weigh over a hundred thousand pounds (over fifty thousand kilograms). If the hook block is horizontal, then it may be difficult and dangerous to handle the wire rope underneath the block. The favored orientation can depend on whether the boom top of the crane is positioned directly over the block or a short distance away from it horizontally.
Reeving is then done by passing the wire rope from one side of the block around a sheave to the other side of the block, and then around a sheave in the boom top, and so on until reeving through all of the desired sheaves is complete. Reeving the hook block is made easier when the sheaves are within reach of a person standing on the ground. Care needs to be taken during reeving not to pull too hard on the ropes, or at an angle, to prevent the block from tipping over. Care should also be taken not to let the wire rope rub against any fixed edges like those of plates, tie bolts, or cross bars that could damage the wire rope.